1. Field of the Invention
The present invention relates to an optical rod for making uniform the irradiation of light emitted from a light source, a manufacturing method thereof, a jig for manufacturing an optical rod, and a projector equipped with such an optical rod.
2. Description of the Related Art
FIG. 7 is a side view illustrating a conventional illumination light source system. In FIG. 7, an illumination light source system 900 comprises a light source 910 and a tubular optical rod (integrator rod) 920. Outgoing light 901 emitted from the light source 910 enters the tube from one end 921 of the optical rod 920 and is reflected on inner walls of the tube.
The number of reflections varies with the angle of incidence of the light beam entering the optical rod 920. Beams subjected to a different number of reflections are all superposed at an end 922 of the optical rod 920, from where the light beams emerge. At this time, the intensity of the superposed light beams becomes almost uniform on the surface at the end 922, from where the beams emerge. By then transferring the superposed beams directly onto an illumination area, such as a display panel, uniform illumination can be achieved.
FIG. 8 is an elevation view illustrating an optical rod according to the conventional art 1. As illustrated in FIG. 8, an optical rod 930 has a pair of vertical reflector plates 932 and 934 disposed in parallel and sandwiched between the two ends of a pair of horizontal reflector plates 931 and 933, in such a manner as to form a tubular body having a substantially rectangular cross-section (for example, the width in the horizontal direction is 8.4 mm, the height in the vertical direction is 7 mm, the length in the depth direction 25 mm, and the plate thickness 1.1 mm).
FIG. 9 is an elevation view illustrating an optical rod according to the conventional art 2. As illustrated in FIG. 9, the optical rod 940 has a pair of vertical reflector plates 942 and 944 vertically disposed and sandwiched between stepped portions 941c and 943d, and 941d and 943c at both ends of a pair of horizontal reflector plates 941 and 943, respectively, in such a manner as to form a tubular body having a substantially rectangular cross-section.
In the case of an optical rod as shown in FIG. 9, since the dimensional accuracy of inner walls of the optical rod is greatly affected by the dimensional accuracy of end surfaces 942a and 942b, and 944a and 944b of the vertical reflector plates 942 and 944, respectively, and the dimensional accuracy of the step portions 941c and 941d, and 943c and 943d of the horizontal reflector plates 941 and 943, respectively, precise machining, including polishing, is required on both the horizontal reflector plates and the vertical reflector plates.
It is essential to precisely control the angle and the spacing of the reflecting surfaces of an optical rod in order that the beams subjected to internal reflections in the optical rod may be uniformly superposed on the surface at the end from where the beams emerge. For this reason, the conventional art 1 requires high-precision machining, including polishing, because the dimensional accuracy of the inner walls of the optical rod is greatly affected by that of the end surfaces 932a and 932b, and 934a and 934b of the vertical reflector plates 932 and 934, respectively. Optical rods of this type are vulnerable to an external force applied to the vertical reflector plates in the vertical direction, and particularly so in the case where the width of the horizontal reflector plate (that is, the distance between the two end surfaces of the horizontal reflector plate, for instance, the distance between 931a and 931b) is made longer than the normal width. Such a variance in the width results in insufficient adhesive strength because the space where the adhesive is applied becomes reduced, thus making the optical rod more vulnerable to external forces.
In the conventional art 2, although it is possible to increase the strength of the optical rod against an external force exerted on the vertical reflector plates in the vertical direction, the shape of the horizontal reflector plates then becomes more complicated, resulting in such disadvantages as the more precise machining requirements by polishing a larger area more portions, difficult machining and higher costs.